Moulin, M. | Search bioRxiv

bioRxiv2024

Hierarchical structural organization in bioinspired peptide coacervate microdroplets

This study explores the dynamic and hierarchical structural organization of peptide coacervate microdroplets at the meso-to atomic-scale resolution using a combination of Transferred Nuclear Overhauser Effect Spectroscopy (TrNOESY), Small Angle Neutron Scattering (SANS), and confocal microscopy. Dynamic interactions driving the self-association of peptide clusters are revealed, highlighting the critical roles of interacting residues. These phase-separating model peptides form small oligomers at low pH, which aggregate into larger clusters at neutral pH. These clusters organize into a porous network within the droplets, facilitating size-selective cargo sequestration. The findings underscore the significance of the dynamic spatio-temporal properties of peptide-based coacervates, contributing to our understanding of phase separation at the atomic and molecular levels. Critically, this approach enables the investigation of coacervate structures in their native state, offering insights into the physical and dynamic interactions governing droplet formation and cargo encapsulation. TOC O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=106 SRC="FIGDIR/small/602323v4_ufig1.gif" ALT="Figure 1"> View larger version (43K): org.highwire.dtl.DTLVardef@15aadb2org.highwire.dtl.DTLVardef@41be55org.highwire.dtl.DTLVardef@36f0d8org.highwire.dtl.DTLVardef@fe1af8_HPS_FORMAT_FIGEXP M_FIG C_FIG

biochemistry↗

bioRxiv2023

Liver sinusoidal endothelial cells constitute a major route for hemoglobin clearance

Mild rupture of aged erythrocytes occurs physiologically in the spleen, leading to the release of hemoglobin (Hb), while pathological hemolysis characterizes several diseases. The detoxification of Hb has traditionally been attributed to the sequestration of Hb-haptoglobin complexes by macrophages. However, this process remains incompletely studied in animal models or primary cells, leaving the precise mechanisms of Hb clearance elusive. Using mice and primary liver cell cultures (murine and human), we uncovered that Hb uptake is chiefly performed by liver sinusoidal endothelial cells (LSECs) and involves macropinocytosis. Consistently, mouse LSECs displayed proteomic signatures indicative of active heme catabolism, ferritin iron storage, antioxidant defense, and macropinocytic capacity. LSECs also exhibited high iron content and the expression of hepcidin-regulated iron exporter ferroportin. Using erythrocyte/Hb transfusion assays in mice, we demonstrated that while splenic macrophages excel in phagocytosis of erythrocytes, LSECs primarily scavenge Hb and Kupffer cells clear erythrocyte membranes, the spleen-borne hemolysis products delivered to the liver via the portal circulation. High-dose Hb injections resulted in transient hepatic iron retention, early LSEC-specific induction of heme-catabolizing Hmox1 and iron-sensing Bmp6, culminating in hepcidin-mediated temporary hypoferremia. Transcriptional induction of Bmp6 in mice was phenocopied by erythrocyte lysis upon phenylhydrazine or iron citrate injection, although the latter elicited a distinct LSEC transcriptional signature compared to Hb. In conclusion, we identify LSECs as key Hb scavengers, a function that establishes the spleen-to-liver axis for iron recycling and contributes to heme detoxification during hemolysis, coupled with the induction of the BMP6-hepcidin axis to restore iron homeostasis.

cell biology↗